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Subject: [RFC PATCH 02/12] netfs: Add an iov_iter to the read subreq for the
 network fs/cache to use
From:   David Howells <dhowells@redhat.com>
To:     linux-fsdevel@vger.kernel.org
Cc:     dhowells@redhat.com, Jeff Layton <jlayton@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve French <sfrench@samba.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Mike Marshall <hubcap@omnibond.com>,
        David Wysochanski <dwysocha@redhat.com>,
        Shyam Prasad N <nspmangalore@gmail.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
        linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
        ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
        devel@lists.orangefs.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Date:   Wed, 21 Jul 2021 14:44:53 +0100
Message-ID: <162687509306.276387.7579641363406546284.stgit@warthog.procyon.org.uk>
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References: <162687506932.276387.14456718890524355509.stgit@warthog.procyon.org.uk>
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Add an iov_iter to the read subrequest and set it up to define the
destination buffer to write into.  This will allow future patches to point
to a bounce buffer instead for purposes of handling oversize writes,
decryption (where we want to save the encrypted data to the cache) and
decompression.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/file.c          |    6 +-----
 fs/netfs/read_helper.c |    5 ++++-
 include/linux/netfs.h  |    2 ++
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index c9c21ad0e7c9..ca529f23515a 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -319,11 +319,7 @@ static void afs_req_issue_op(struct netfs_read_subrequest *subreq)
 	fsreq->len	= subreq->len   - subreq->transferred;
 	fsreq->key	= subreq->rreq->netfs_priv;
 	fsreq->vnode	= vnode;
-	fsreq->iter	= &fsreq->def_iter;
-
-	iov_iter_xarray(&fsreq->def_iter, READ,
-			&fsreq->vnode->vfs_inode.i_mapping->i_pages,
-			fsreq->pos, fsreq->len);
+	fsreq->iter	= &subreq->iter;
 
 	afs_fetch_data(fsreq->vnode, fsreq);
 }
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 0b6cd3b8734c..715f3e9c380d 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -150,7 +150,7 @@ static void netfs_clear_unread(struct netfs_read_subrequest *subreq)
 {
 	struct iov_iter iter;
 
-	iov_iter_xarray(&iter, WRITE, &subreq->rreq->mapping->i_pages,
+	iov_iter_xarray(&iter, READ, &subreq->rreq->mapping->i_pages,
 			subreq->start + subreq->transferred,
 			subreq->len   - subreq->transferred);
 	iov_iter_zero(iov_iter_count(&iter), &iter);
@@ -745,6 +745,9 @@ netfs_rreq_prepare_read(struct netfs_read_request *rreq,
 	if (WARN_ON(subreq->len == 0))
 		source = NETFS_INVALID_READ;
 
+	iov_iter_xarray(&subreq->iter, READ, &rreq->mapping->i_pages,
+			subreq->start, subreq->len);
+
 out:
 	subreq->source = source;
 	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index fe9887768292..5e4fafcc9480 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -17,6 +17,7 @@
 #include <linux/workqueue.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>
+#include <linux/uio.h>
 
 /*
  * Overload PG_private_2 to give us PG_fscache - this is used to indicate that
@@ -112,6 +113,7 @@ struct netfs_cache_resources {
 struct netfs_read_subrequest {
 	struct netfs_read_request *rreq;	/* Supervising read request */
 	struct list_head	rreq_link;	/* Link in rreq->subrequests */
+	struct iov_iter		iter;		/* Iterator for this subrequest */
 	loff_t			start;		/* Where to start the I/O */
 	size_t			len;		/* Size of the I/O */
 	size_t			transferred;	/* Amount of data transferred */